1. Technical Field of the Invention
The present invention relates to a method and apparatus for recognizing presence of objects from the detection results obtained from a laser radar system, and in particular, the method and apparatus preferably applied to vehicles.
2. Related Art
Object recognition apparatus have been known. For example, in a known object recognition apparatus, an object (mainly, a preceding vehicle) residing in the forward direction of the vehicle concerned is recognized to perform a vehicle control, such as an adaptive cruise control (ACC) or a control based on a pre-crash safety system (PCS).
For example, JP-A-2004-053278 discloses this type of object recognition apparatus. This object recognition apparatus includes a laser radar system and an imaging unit. The laser radar system sequentially emits laser beams (i.e. probe waves) along a predetermined scan direction so that the beams are adjacently juxtaposed. Then, an object as an object to be detected is recognized based on the results of the emission of the laser beams. Meanwhile, the imaging unit picks up an image that includes, as an imaging range, at least a scan area of the laser beams. Then, the picked up image is subjected to an image recognition process so that an object to be detected is recognized. In such an object recognition apparatus, the location of the object to be detected, which has been recognized by each of the laser radar system and the imaging unit is traced in a time-series manner.
In the object recognition apparatus, the laser radar system (hereinafter referred to as “conventional radar system”) generates a measured-distance datum every time a laser beam is emitted, based on a reflected wave from an object, which wave is obtained as a result of the emission of the laser beam. The measured-distance datum includes the location of the object (i.e. a distance from the laser radar system to the object, a coordinate in the widthwise direction of the vehicle, and a coordinate in the heightwise direction of the vehicle).
The location of the object may be different between measured-distance datums. Those measured-distance datums forming an area and having the above difference of not more than a preset allowable value are grouped as belonging to the same group. Then, the location of the grouped measured-distance datums, or a group of measured-distance datums, is traced in a time-series manner to recognize an object to be detected. This is the generally performed process of object recognition.
FIG. 7A is a diagram illustrating the travel conditions of vehicles A and B traveling on a road in the forward direction of the vehicle concerned. FIG. 7B is a diagram illustrating the states of measured-distance datums that have been recognized as being the vehicles A and B by the conventional radar system under the travel conditions illustrated in FIG. 7A.
As shown in FIG. 7A, the vehicle B traveling from behind the vehicle A at time t approaches the vehicle A at time t+1. Then, at time t+2, the vehicle B, with its end portion (left end) approaching an end portion (right end) of the vehicle A, eventually travels side by side with the vehicle A. Then, at time t+3, the vehicle B travels ahead of the vehicle A.
At times t, t+1 and t+3 under such conditions, the difference between the measured-distance datum corresponding to the end portion (right end) of the vehicle A and the measured-distance datum corresponding to the end portion (left end) of the vehicle B is larger than an allowable value. Therefore, as shown in FIG. 7B, the conventional radar system separately groups the measured-distance datums corresponding to the vehicle A and the measured-distance datums corresponding to the vehicle B to individually recognize the vehicles A and B.
On the other hand, at time t+2, the distance from the conventional radar system to the vehicle A is equal to the distance to the vehicle B. Also, since the vehicle B has approached the vehicle A, the distance between the end portion (right end) of the vehicle A and the end portion (left end) of the vehicle B becomes small in the widthwise direction of the vehicle (hereinafter just referred to as “widthwise direction”).
Meanwhile, a laser beam emitted from the conventional radar system is scattered as the distance after the emission becomes longer, allowing the beam width to be larger. Therefore, the laser beam emitted toward the space between the vehicles A and B may not pass through the space between the vehicles A and B but may be reflected by the vehicle A or the vehicle B. In such a case, in the conventional radar system, the difference between the measured-distance datum detected as the end portion (right end) of the vehicle A and the measured-distance datum detected as the end portion of the vehicle B becomes equal to or less than the allowable value. As a result, the measured-distance datums of the vehicles A and B are grouped as a single object (i.e. a single vehicle). This raises a problem that the two vehicles A and B are erroneously recognized as a single object.
Moreover, in the time-series tracing of the locations of the vehicles A and B using the conventional radar system, the tracing is kept with the vehicles A and B being erroneously recognized. Therefore, there has been a problem that, at time t+2, the behaviors of the erroneously recognized vehicle as an object are regarded as skidding, or the size of the vehicle as an object is recognized as having become suddenly large.
In other words, the conventional radar system has suffered a problem that, when more than one object to be detected is closely located along the scan direction, the individual objects to be detected cannot be recognized with good accuracy.